Canadian Hydrological Drought: Processes and Modelling John Pomeroy, Robert Armstrong, Kevin Shook, Logan Fang, Tom Brown, Lawrence Martz Centre for Hydrology,

Canadian Canadian Hydrological Hydrological

Drought:Drought: Processes and Processes and

ModellingModellingJohn Pomeroy, Robert Armstrong, Kevin Shook, John Pomeroy, Robert Armstrong, Kevin Shook,

Logan Fang, Tom Brown, Lawrence Martz Logan Fang, Tom Brown, Lawrence Martz

Centre for Hydrology, Centre for Hydrology, University of Saskatchewan,University of Saskatchewan,

SaskatoonSaskatoon

Prairie Hydrology - Prairie Hydrology - RealityReality

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Smith Creek, Saskatchewan

OverviewOverview OBJECTIVEOBJECTIVE

To better understand, describe and model the To better understand, describe and model the development of hydrological drought on the development of hydrological drought on the PrairiesPrairies

FOCUS – evaluation and drought sensitivity ofFOCUS – evaluation and drought sensitivity of ProcessesProcesses

Snow Redistribution, Accumulation and MeltSnow Redistribution, Accumulation and Melt Runoff Generation/Wetland RechargeRunoff Generation/Wetland Recharge Areal EvaporationAreal Evaporation

ModellingModelling Prairie Hydrological Modelling – CRHM platform to Prairie Hydrological Modelling – CRHM platform to

create physically based hydrological models of soil create physically based hydrological models of soil moisture, evaporation, snow accumulation, small prairie moisture, evaporation, snow accumulation, small prairie stream runoff and wetland rechargestream runoff and wetland recharge

Calculating Prairie Snowmelt RunoffCalculating Prairie Snowmelt Runoff

Spatially distributed Spatially distributed blowing snow modelblowing snow model 262,144 grids262,144 grids On each grid calculation On each grid calculation

of fluxes based on of fluxes based on

St Denis, Saskatchewan

Spatially Distributed Blowing Snow Spatially Distributed Blowing Snow Accumulation - FebAccumulation - Feb

Spatially Distributed Blowing Snow Spatially Distributed Blowing Snow Accumulation – End of MarchAccumulation – End of March

Blowing Snow in Blowing Snow in Operational Drought Operational Drought

ModellingModelling For hydrological and agricultural water balance For hydrological and agricultural water balance applications, need landscape type specific calculations, applications, need landscape type specific calculations, aggregated approachaggregated approach

To calculate mass balance for landscape unit (TILE), To calculate mass balance for landscape unit (TILE), need inputs from upwind tiles (source to sink)need inputs from upwind tiles (source to sink)

Possible to calculate transport from one tile to anotherPossible to calculate transport from one tile to another Calculation order based on tile aerodynamic sequence (smooth Calculation order based on tile aerodynamic sequence (smooth

to rough; high elevation to low elevation). Transport to rough; high elevation to low elevation). Transport outout from from one tile is transport one tile is transport inin to next tile. to next tile.

Important to preserve continuity at multiple scalesImportant to preserve continuity at multiple scales

Fallow Field

Stubble Field

Grassland Brush Trees

Spatially Aggregated Blowing Snow Spatially Aggregated Blowing Snow Accumulation, 7 tilesAccumulation, 7 tiles

Distributed vs Aggregated Blowing Snow Distributed vs Aggregated Blowing Snow ModellingModelling

Areal average SWE from two resolutions of blowing snow model and snow surveys

distributed = 111 mm, aggregated = 90 mm, and observed = 97 mm.

Prairie EvaporationPrairie Evaporation Actual Evaporation critical component of droughtActual Evaporation critical component of drought Uncertainty in estimating EvaporationUncertainty in estimating Evaporation

Various theoretical relationships with differing sets of Various theoretical relationships with differing sets of parameters (parameters (αα, z, zoo, d, vegetation, water), variables (K↓, , d, vegetation, water), variables (K↓, L↓, u, T, q) and state variables (L↓, u, T, q) and state variables (θθ, T, Tss) )

Highly spatial variability) – Highly spatial variability) – subgrid variabilitysubgrid variability Advection to pondsAdvection to ponds

Aggregation in LSS.Aggregation in LSS. TilesTiles Problem of changing tile area during droughtProblem of changing tile area during drought

ContinuityContinuity All models limit water for evaporation by tracking All models limit water for evaporation by tracking

supplysupply Prairie plants don’t care and send roots to available Prairie plants don’t care and send roots to available

water (+3 m)water (+3 m)

Field Observation Field Observation NECESSARYNECESSARY

St Denis National Wildlife Area, Saskatchewan

• St Denis, SK, summer 2006, dry but no drought• 3 physically based methods (Granger GD, Penman-Monteith, Dalton Bulktransfer {LSS-like} compared to best observation sets from eddy correlation.• Possible to set soil moisture for resistance and continuity aspects of CRHMfrom field measurements of soil water (no model calibration).

Evaporation for Optimal Periods at St. Denis (2006)

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Lethbridge Ameriflux Site (2001)Lethbridge Ameriflux Site (2001)

EnteredDrought as summer 2001Progressed

Severe Decline in Soil water content anddaily actual evaporation

• Modeling evaporation under drought conditions requires soil moisture accounting• Influence of canopy resistance term increases as season progresses• Uncertainty in reference minimum for resistance – PM, BT• Not possible to set physically realistic parameters for Penman-Monteith and

Dalton Bulk Transfer resistance schemes, • Granger GD method in CRHM performed well in severe drought

• Important for hydrology•Wetland recharge and dessication•Streamflow generation, contributing area for runoff

• Two eddy correlation systems, 2007, pond and dryland

Spatial Variability of Prairie Evaporation

Land vs Water Evaporation at Pond 1 (St. Denis, 2007)

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Thermal Image of St. Denis NWA (2007)Taken from an infrared imager from an airplane

Island

Mixed Grasses

Cultivated

Pond 90

wetlands

Trees

Aug 5, 2007;12:12 pm

road

Provides basis for spatial distribution of net radiation in Granger GD evaporation method

Distributed Daily Evaporation St Denis

Distributed:-Outgoing longwave-Outgoing shortwave-Aerodynamic roughness

Granger GD Modelwith “common”atmospheric feedback, T, RH,

Spatial Frequency Spatial Frequency Distribution of Actual Distribution of Actual Evaporation (one day)Evaporation (one day)

wetlanddryland

mm daily actual evaporation

Cold Regions Hydrological Cold Regions Hydrological Model Process ModulesModel Process Modules

Developed from research at University of Developed from research at University of Saskatchewan and EC over several decadesSaskatchewan and EC over several decades

Radiation (slopes, estimation procedures)Radiation (slopes, estimation procedures) Blowing snow (snow transport & sublimation)Blowing snow (snow transport & sublimation) Interception (rain and snow)Interception (rain and snow) Snowmelt (open & forest, advection, energy Snowmelt (open & forest, advection, energy

balance)balance) Infiltration (frozen and unfrozen soils)Infiltration (frozen and unfrozen soils) Evaporation (Granger or Penman-Monteith)Evaporation (Granger or Penman-Monteith) Soil moisture balance (with groundwater Soil moisture balance (with groundwater

interaction)interaction) Routing (hillslopes, sub-surface and streamflow)Routing (hillslopes, sub-surface and streamflow)

CRHM Use for DRICRHM Use for DRI

Hydrological evolution and feedbacks in Hydrological evolution and feedbacks in droughtdrought

Hydrological Drought Indices based on small Hydrological Drought Indices based on small basin soil moisture, streamflow and wetland basin soil moisture, streamflow and wetland levelslevels

Scaling methodology and process test bedScaling methodology and process test bed Evaluate prairie land surface Evaluate prairie land surface

parameterisations and aggregation for parameterisations and aggregation for MESHMESH

Develop prairie hydrology routing for MESHDevelop prairie hydrology routing for MESH Provide drought hydrology tool for usersProvide drought hydrology tool for users

1999-2004/05 Drought I1999-2004/05 Drought Impact at St. Denis, cumumpact at St. Denis, cumulative effect on the hydrolative effect on the hydro

logical processeslogical processesand wetland water leveland wetland water levelmodelled with CRHMmodelled with CRHM

CRHM Test at Wetland 109, St DenisCRHM Test at Wetland 109, St Denis

CRHM Application to CRHM Application to PrairiesPrairies

Apply to two representative types of basins Apply to two representative types of basins (RB)(RB) Well drained small prairie streamWell drained small prairie stream Wetland basin with much surface storageWetland basin with much surface storage Create prairie drought surface of basin state Create prairie drought surface of basin state

variablesvariables Need standard atmospheric observations Need standard atmospheric observations

or reanalysis data (U,T, RH, Precip) or reanalysis data (U,T, RH, Precip) Needs radiation (sparse observations!!!)Needs radiation (sparse observations!!!) Calculates soil moisture, streamflow, water Calculates soil moisture, streamflow, water

storage, snowpack as state variablesstorage, snowpack as state variables

NARR Daily QsiNARR Daily Qsi

NARR => CRHM Simulated NARR => CRHM Simulated Hourly QsiHourly Qsi

Creating Frequency Creating Frequency Distributions of Wetlands for Distributions of Wetlands for

Hydrological Modelling of Hydrological Modelling of Prairie Wetland Prairie Wetland

Representative BasinRepresentative Basin Need to have characteristic Need to have characteristic frequency distribution of wetlands – frequency distribution of wetlands – this changes during drought.this changes during drought.

Test at St Denis where excellent Test at St Denis where excellent data exists……data exists……

Simply route water excess along Simply route water excess along surface topography from one storage surface topography from one storage area to the nextarea to the next

0.1 m water added to 0.1 m water added to DEMDEM

0.3 m water added to 0.3 m water added to DEMDEM

St. Denis Slough St. Denis Slough SimulationSimulation

Runoff from spatially-constant precip - spatially-constant Evap.

Need spatially variableevaporation

ConclusionsConclusions Successful physically-based prairie hydrological Successful physically-based prairie hydrological

modelling for small basins using CRHM – no calibrationmodelling for small basins using CRHM – no calibration Spatial scale for blowing snow accumulation and spring Spatial scale for blowing snow accumulation and spring

runoff calculation determined – tiled approach runoff calculation determined – tiled approach adequateadequate

Suppression of blowing snow transport and Suppression of blowing snow transport and enhancement of frozen soil infiltration responsible for enhancement of frozen soil infiltration responsible for much of wetland desiccation in droughtmuch of wetland desiccation in drought

Evaluation of evaporation models and observations Evaluation of evaporation models and observations suggests that soil moisture should be a product rather suggests that soil moisture should be a product rather than a driver of evaporation calculations. Possible to than a driver of evaporation calculations. Possible to distribute Granger method.distribute Granger method.

Spatial distribution of evaporation, pond storage and Spatial distribution of evaporation, pond storage and runoff provides basis for upscaling atmospheric runoff provides basis for upscaling atmospheric feedbacks and calculating hydrology in drought.feedbacks and calculating hydrology in drought.

CRHM ready for application to develop Prairie-wide CRHM ready for application to develop Prairie-wide hydrological drought products, Representative Basin hydrological drought products, Representative Basin soil water, runoff, water storagesoil water, runoff, water storage